« ПретходнаНастави »
241. A Nautical Almanack is published by government, expressly for the use of sailors; and is carried, in many curious particulars, to such a nicety, that by means of his octant, a telescope, and an accurate watch or time-piece, a sailor can now ascertain his position in any part of the seas within half a mile.
242. So expert are navigators become in our days, that a ship has sailed from Portsmouth to Caleutta in 55 days, a voyage which formerly employed six months; from Portsmouth to Malta in 11 days, formerly two months; to New York in 21 days, formerly two months; and to the West Indies in 21 days, formerly two months.
Drake and Anson were three years in sailing round the world, and this is now frequently performed by merchantmen, in nine or ten months.
XIII. Geography and Astronomy. 243. Geography describes the surface of the earth ; the shape and size of the land and seas; the boundaries of nations, and their climate and natural productions.
It also teaches the character of the inhabitants; their government, religion, manufactures, and mode of living; and it ought to enable us to shun their errors, and profit by their experience.'
Obs.-As there are numerous works adapted for schools on this subject, and the details are very extensive and prolix, it would be trifling with the pages of this work, to dwell tediously on geography,
244. The earth, on which we live, is a round ball or globe, 8,000 miles in diameter, and 25,000 miles round. Its surface is covered with one part of land, and three parts of water, which are inhabited and filled with innumerable living creatures.
245. Of the internal parts of this immense globe little is known to us.
From the surface to the centre is 4,000 miles, yet no mine is a mile deep.
As far as man has penetrated, he has found successive layers or coats of different earths ; laying over each other, like the coats of an onion, or the leaves of a book.
Obs.-In digging wells, various thicknesses of different soils are found in different places, in an order something like the following: three feet of black earth, called vegetable mould, four of gravel, five of gravel and sand, six of clay, three of sea-shells, fifty feet of clay, forty of sand, five of stone, three of marl, &c. &c. and what is remarkable, every layer is the same thickness as far as it extends, and generally parallel with the surface of the earth.--See my Grammar of Philosophy.
246. The highest mountains detract no more from the roundness of the earth than the inequalities on the rind of an orange detract from its general rotundity. Chimborazo, one of the Andes, rears its lofty head four miles high, yet this is but the two tkousandth part of the earth's diameter.
Obs.-Mount Blanc is not three miles high; the Peake of Teperiffe but two miles and a half; and Mount Etna not two miles. The Snowdon, in England, is not three quarters of a . mile; and but a grain of sand compared to the whole earth.
247. The mines, therefore, may be compared to the sting of a bee in the body of an elephant ; and the mountains to the inequalities in the rind of an orange: yet, vast as is the earth, the sun, which enlightens and warms it, is one million times greater; or, in other words, one million earths united in one mass, would only be the size of the sun.
248. The land consists of two continents; the old continent of Europe, Asia, and Africa, and the lately discovered continent of America.
There are also many thousand islands surrounded by the sea; many of them, as Great Britain, it is supposed were anciently united to the continent, and others, the tops of marine mountains peeping out of the
sea, the bases of which are at the bottom of the
249. When a point of land juts out into the sea, it
is called a Cape or Promontory; as the Cape of Good Hope.
When two masses of land are joined together by a narrow slip, it is called an Isthmus; as the Isthmus of Suez, and the Isthmus of Panama.
A Peninsula is a tract of land almost surrounded by water : Spain and Portugal are a peninsula.
250. The waters are usually divided into four Oceans; the Great or Pacific Ocean, ten thousand miles across ; the Atlantic Ocean, three thousand miles across; the Indian and Southern Ocean; and the Northern Ocean.
Seas are detached pieces of water; as the Mediterranean and the Baltic.
Gulfs and Bays are parts of the sea that indent into the land; as the Gulf of Mexico, and Chesapeak bay.
And Straits are narrow passes joining one sea or ocean to another; as the Straits of Gibraltar.
251. The vast Sun, to which we are under such sensible obligations, for light, heat, life, and vegetation; and without whose genial influence all the earth would become a dark, solid mass of ice, is 900,000 miles in diameter; and the earth is 95 millions of miles distant from it.
252. The Sun is the centre of a vast system of planets, or globes, like the earth; all of which move round his body at immense distances, in periods which include the various seasons to each, and are therefore a
year to each.
Obs. They are all pressed to each other's centre ; but the action of their fluid parts against their solid parts, gives them a tendency to go forward in a straigbt line; and those two forces so balance each other, that they neutralize one another, and in consequence, the planets are moved round the sun in an orbit which is nearly circular. See 283.
253. The sun has been commonly considered a globe of pure fire. A number of maculæ, or dark
spots, may, however, by means of a telescope, be seen on different parts of his surface.
These consist of a nucleus, which is much darker than the rest, and surrounded by a mist or smoke; and they are so changeable as frequently to vary during the the time of observation.
Some of the largest of them exceed the bulk of the whole earth, and they are often seen for three months together.
They are supposed to be cavities in the body of the sun; the nucleus being the bottom of the excavation ; and the shady zone surrounding it, the shelving sides of the cavity.
THE SUN AND SOME OF HIS SPOTS.
Great source of day! best image here below
254. As the sun is one million times larger than the earth, it is evident that the balance of their mutual
pressure would not be destroyed, if one million of earths moved round the sun ; but at present, we know only of seven such bodies, some nearer and some farther off than the earth, and some greater, and some smaller, called Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Herschel.
The Sun revolving on his axis turns, And with creative fire intensely burns ; First Mercury completes his transient year, Glowing, refulgent, with reflected glare; Bright Venus occupies a wider way, The early harbinger of night and day ; More distant still our globe terraqueous turns, Nor chills intense, nor fiercely heated burns ; Around he rolls the lunar orb of light, Trailing her silver glories through the night. Beyond our globe, the sanguine Mars displays, A strong reflection of primeval rays ; Next belted Jupiter far distant gleams, Scarcely enlightened with the solar beams; With four unfix'd receptacles of light, He towers majestic through the spacious beight; But farther yet, the tardy Saturn lags, And seven attendant luminaries drags; Investing with a double ring his pace, He circles through imwensity of space.-CHATTERTON. 255. Some of these several globes, so revolving to receive light and heat from the sun, serve as centres to other minor globes called moons. These satellites accompany
the planet in its tour round the sun; serving to balance its motions, and to reflect by night the sun's light on the planet for the use of the inhabitants.
256. The earth has one moon, 2,000 miles in diameter, and a quarter of a million of miles distant from the earth.
Jupiter, another planet, has four moons.
Saturn seven moons; and he is also surrounded by a large double ring, 30,000 miles distant from his body.
And Herschel has six moons.